This invention relates to pads for supporting the seated and recumbent human body which redistribute body weight away from bony prominent areas, which areas are the most susceptible to the formation of pressure ulcers and, in particular, to convoluted foam pads used for this purpose.
Two of the primary causes of pressure ulcers are pressure and moisture The pressure results from the supporting surface resisting the force of gravity on the body. For mattresses, this pressure is typically the highest beneath the shoulder (the scapulae) and tail (the sacrum and trochanter), generally the areas of greatest mass and projection. In these high pressure areas, the pressure against the body can be sufficient to occlude the capillaries and lymph vessels, thereby preventing the circulation of oxygen and nutrients to the skin. In addition, because airflow over these skin areas is typically prevented due to the surface of the mattress, greater amounts of moisture are excreted for the dissipation of heat and waste. Over a sufficient period of time, the combination of high pressure and moisture will lead to the formation of pressure ulcers.
In an effort to combat the formation of pressure ulcers among patients, hospitals utilize a number of types of bed pads for their patients who fall into high risk categories. These products include static air, water and foam support pads. Although these pads cannot reduce the overall resistance of the mattress to the weight of the body, they can reduce the level of pressure on the areas of highest pressure by redistributing the load and allowing a greater portion of the pad to support the body. Each of these types of pads has different advantages and disadvantages.
Generally, static air and water support pads provide superior high pressure reduction capabilities at the bony prominences, but permit only limited air flow and heat dissipation. In addition, both static air and water support pads require filling, are susceptible to leaks and tend to "bottom out" (i.e., permit the weight of the user to displace the air or water in the pad to the extent that the user is supported by the mattress, rather than by the air or water cushion). Static water support pads also are undesirable in that they are heavy and unwieldy to transport. While pumps and valves can be used to vary the pressure resistance of the static air and water pads over time, these features render the pad both expensive and difficult to install and transport.
Convoluted foam pads, on the other hand, are generally relatively inexpensive and easily transported, while providing superior air flow potential and moisture reduction capabilities. Unfortunately, despite considerable study and effort, it has proved exceedingly difficult to develop an easily manufactured convoluted foam pad which is capable of providing pressure reduction characteristics comparable to static air and water support pads.
The manufacture of convoluted foam pads continues to largely follow the methods taught by U.S. Pat. No. 3,431,802, which patent is hereby incorporated by reference. The pads are typically formed by feeding a foam block between two cooperating parallel cylinders, each of which has a undulated surface. The cylinders rotate towards one another and are spaced so that the block inserted between them is compressed between the cylinders and is driven against a cutting edge which slices the block in half. Each half generally comprises alternating rows of peaks and valleys, in checkerboard fashion. The resulting halves are perfectly matched so that when one half is laid upon the other, the tops of the peaks of one half rest against the floor of the valleys of the other half forming a solid block. In addition, although it is possible to manufacture pads which are not the mirror image or reflection of one another, this is rarely done, as it would typically result in only one usable half, thereby significantly increasing material costs.
One convoluted foam pad currently in use is disclosed in U.S. Pat. No. 4,686,724. The pad is comprises alternating columns of peaks and valleys in checkerboard fashion. Air channels are stamped, press cut or laser cut through the floor of the valleys to the bottom face of the pad, leaving removable plugs used to selectively control the amount of aeration and dissipation of body heat permitted by the pad.
In one embodiment, the peaks of the pad are "topped off" to create a broken flat surface, interposed with valleys, with the distance between the floor of each valley and the bottom surface of the pad being constant. Within each valley is a channel extending from the valley floor to the flat bottom face of the pad. The patent teaches that a skin area of 1.25 inches in diameter or less, even though denied air circulation, can sustain itself from air circulating in an adjacent area. Therefore, by limiting each peak top to a diameter of 1.25 inches or less, the occurrence of decubitus ulcers can, according to the patent, be virtually eliminated. Unfortunately, the use of this uniform pad with its removable plugs has found little acceptance in practice, perhaps because the removal and replacement of the individual plugs is relatively difficult and time consuming.
A second convoluted foam pad is disclosed in U.S. Pat. No. 4,620,337. The pad is designed to prevent the formation of decubitus ulcers by minimizing the amount of pressure exerted on the body. The pad has three distinct sections: a convoluted head supporting section; a ribbed torso supporting section; and a convoluted foot and leg supporting section. As with most foam pads which are manufactured from a block of uniform thickness, the sum of the distance from the bottom face of the pad to the top of any peak (the "peak height") and the distance from the bottom face of the pad to the floor of any valley (the "base height" or "valley floor height") remains constant. This arises from the fact that although the height of the undulating surface of the paired cylinders varies along their length, the opposing undulating surfaces are of an equal height.
The pad is designed on the premise that heavier portions of the body are less likely to develop pressure ulcers when they are supported by a portion of the pad with a lower peak to base ratio, and that lighter portions of the body are less likely to develop pressure ulcers when they are supported by a portion of the pad with a higher peak to base ratio. Accordingly, the ribs of the torso supporting section are shorter than the average height of the peaks of the head or leg supporting sections, and the floors of the valleys of the torso supporting section are higher than the average height of the floors of the valleys of the head or leg supporting sections. Unfortunately, however, the pressure reduction capabilities of this pad are significantly lower than the pressure reduction capabilities of static air or water support pads.
What is needed, therefore, is a convoluted foam pad which is easy to manufacture and provides high pressure area reduction capabilities comparable to the static air and water support pads.